Wireless communication systems provide for radio communication links to be arranged within the system between a plurality of user terminals. Such user terminals may be mobile and may be known as ‘mobile stations’ or ‘subscriber units.’ At least one other terminal, e.g. used in conjunction with subscriber units, may be a fixed terminal, e.g. a control terminal, base station, repeater, and/or access point. Such a system typically includes a system infrastructure which generally includes a network of various fixed terminals, which are in direct radio communication with the subscriber units. Each of the base stations operating in the system may have one or more transceivers which may, for example, serve subscriber units in a given local region or area, known as a ‘cell’ or ‘site’, by radio frequency (RF) communication. The subscriber units that are in direct communication with a particular fixed terminal are said to be served by the fixed terminal. In one example, all radio communications to and from each subscriber unit within the system are made via respective serving fixed terminals. Sites of neighboring fixed terminals in a wireless communication system may be offset from one another or may be non-overlapping or partially or fully overlapping.
Wireless communication systems may operate according to an industry standard protocol such as, for example, the Project 25 (P25) standard defined by the Association of Public Safety Communications Officials International (APCO), or other radio protocols, such as the TETRA standard defined by the European Telecommunication Standards Institute (ETSI), the Digital Private Mobile Radio (dPMR) standard also defined by the ETSI, or the Digital Mobile Radio (DMR) standard also defined by the ETSI. Communications in accordance with any one or more of these standards, or other standards, may take place over physical channels in accordance with one or more of a TDMA (time division multiple access), FDMA (frequency divisional multiple access), or CDMA (code division multiple access) protocol. Subscriber units in wireless communication systems such as those set forth above send speech and data, herein referred to collectively as ‘traffic information’, in accordance with the designated protocol.
Many so-called “public safety” wireless communication systems provide for group-based radio communications amongst a plurality of subscriber units such that one member of a designated group can transmit once and have that transmission received by all other members of the group substantially simultaneously. Groups are conventionally assigned based on function. For example, all members of a particular local police force may be assigned to a same group so that all members of the particular local police force can stay in contact with one another, while avoiding the random transmissions of radio users outside of the local police force.
Typically, such groups are assigned a fixed priority, and with the exception of emergency calls and all-calls (e.g., a call to all active members in a wireless communication network), each group is assigned a same priority as other groups and if one or more other groups are already using all available RF resources at a site at which a group member resides, a particular group may be unable to initiate a new group call to all of its members when needed or desired. Furthermore, once a particular talk group is already granted an RF resource (e.g., a pair of an uplink channel and a downlink channel, separated by frequency, time, or code), the RF resource is generally reserved for a short time period after it was last used by a member of the talk group to allow for another talk group member to respond to the prior speaker (hereinafter referred to as a “call hang-time”). Call hang-time is generally configured at the system level and may be set, for example, to three (3) seconds. After the call hang-time has expired, any other group can start a new group call and effectively consume the RF resource that was being used by the previous talk group (e.g., those RF resources are now no longer available to the previous talk group). Accordingly, any member of the previous talk group wishing to further communicate with the previous talk group after the call hang-time would need to go through an entirely new call set-up process, and be subject to a possible lack of sufficient RF resources to start the new group call.
Accordingly, a system and method is needed for two-way radio systems to allow for reserved virtual radio conference calls such that RF resources are reserved at one or more radio sites for all group members participating in the virtual radio conference call, and such that the RF resources reserved for the group are not made available to other groups or subscriber units during the predetermined duration of the virtual radio conference call.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present disclosure.